Toll line switching for prefered subscribers in telephone systems



Sept. 3, 1957 A. B RANDSTETTER ETAL 2,

TOLL LINE SWITCHING FOR PREFERRED SUBSCRIBERS IN TELEPHONE SYSTEMS Filed Sept. 14, 1953 2 Shets-Sheet 1 Fig.1'

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TOLL LINE SWITCHING FOR PREFERRED SUBSCRIBERS IN TELEPHONE SYSTEMS Filed Sept. 14, 1953 2 Sheets-Sheet 2 Km E nfa :2 Sn m? h n Mm $2 .i. 5? N. Q F L 21: n )flfilw 5 N; Na Emm N 1% fi m 5 .81 3 r [Em n Z fi a m 8886f TOLL LINE'SWITCK-HNG F63 PREFERRED SUB- SCREERS IN TELEi HQNE SYSTEMS Alois Brandstetter and Walter Rufer, Munich, Germany, assignors to Siemens & Halshe Aktiengesellsehait, Munich, Germany, a corporation of Germany Application'September 14, 1953, Serial No. 37%,962

Claims priority, application Germany January 9, 1953 2 Claims. (til. 179-27) This invention relates to signaling 0r telecommunica tion systems and is particularly concerned with telephone systems comprising circuit means for switching trunks or toll lines to special or preferred subscribers. The trunk or toll lines may be of substantial length and may include amplifiers if desired. The trunk or toll lines terminate in exchange operators positions atboth ends. it should be understoodthat the term trunk .or toll lines is intended to include physical trunk lines and also carrier frequency lines and radio links.

it is knownto provide circuit means for switching such lines from their normal connectionsto preferred subscribers at both ends, such switching-over being efiected automatically upon the transmission of special criteria by a calling. preferred subscriber and evaluation of these criteriainswitch-over apparatus.

In systems of this. type, it is necessary to insure traflic betweenthe preferred subscribers under all circumstances, even..in..the event of non-functioning of' the switch-over apparatus at eitherend of the line, for exampledue to failure-of the current supply therefor, failure of the sound frequency generators, amplifiers or receivers required for transmittingthecriterion, or for'any other causes.

In accordance with the present invention, this is accomplished by providing the operators positions with switchingrneans which indicate any non-functioning of the switch-overapparatus and which, upon being actuated bythe toll operator, maintain the toll line switched through to the preferred subscriber while simultaneously connecting an emergency current supply into the circuit for this preferred subscriber.

This arrangement has the advantage that the preferred subscribers can establish connections between each other, during breakdowns of the switch-over apparatus, by performing thesame steps as they would carry out during normal functioning. These steps comprise lifting of the receiver and thereafter performing some further manipulation which has the effect of switching-over of the'toll line and completion of the connection between the preferred subscribers. Thus, according to the invention, in the event of failure of the switch-over apparatus, the preferred subscribers need not supplement the abovementioned normal procedural steps by any special open ations such as calling the operator by inductor, nor need they have to be provided with different apparatus such as central-battery or local-battery apparatus.

In accordance with a further feature of the invention, the circuit arrangement is such that, if the operator should fail to notice the trouble signal at the exchange and to establish the continuous connection of the toll line to'the preferred subscriber, a call initiated by the latter will get through to the operators position at the adjacent end of the line. The exchange operator can then converse with the preferred subscriber and thereafter efiect the necessary switching of the toll line through tothis-subscriber. The latter then repeats the usual second step which starts transmission of the ringing current 1 Patented Sep 1957 over the toll line to the preferred subscriber at the other end.

The invention will hereinafter be described with reference to the accompanying drawings in which:

. Fig. l is a block diagram schematically illustratingthe incorporation of the improved switch-over apparatus in a toll line;

Fig. 2shows circuit details of the switch-over appa ratus illustrated in Fig. 1; and

Fig. 3 shows circuit details of the auxiliary service unit associated with the switch-over apparatus of Fig. 2'and located at the exchange operators position.

As will beseen from Fig. 1, the switch-over apparatus Um is inserted in the toll line FL between the terminal amplifier, sound frequency ring converter and the like, which together are designated FV in the drawing, and a relay repeater FS (if any) located at the end of the line. VV designates the pre-amplifier for amplifying the incoming soundfrequency modulated signals; TB is the soundfrequency signal receiver; and Sd is the sound frequency signal transmitter; all of these are part of the switch-over apparatus Um. A link LT serves to connect the special or preferred subscriber ST to the apparatus Um. An auxiliary service unit BS is located at the operators position in the toll exchange FA and is connected with the switch-over apparatus Um over a link L3.

Fig. 1 illustrates the equipment of only one end of the toll line; the arrangement at the other'end of the line 'is exactly the same as that illustrated and has not, therefore, been separately shown.

The manner in which normal connections 'are'made in toll trafic to or from the toll exchange FA, is well known and is not required foran understanding of the present invention; therefore, it will not be particularly described.v In these normal connections, the apparatus Um directly connects links Ll-and L2 with each other and does not perform any special function.

The steps involved in establishing a connection between the preferred subscribers will now be describedwith reference to Fig.' 2.

During idle periods, the relays S and AL-in the apparatus'Um are continuously energized provided the apparatus'is ready to be seized. The energizing circuit'for relay-S extendsover the closed 'contactsls and 2a1 and the conductor lto service unit BS (Fig. 3) and keycontacts TUII and TAI. The circuit forrelay AL is. closed over-contacts of relays that control theavailability of the current supply'for the switch-over apparatus, of the sound frequency generator TG, the'sound frequency receiver TE and other apparatus components. These contacts are symbolized in the drawing by the single contact ux, which is closed as long as the apparatus is ready to be seized.

Seizureof the switch-over apparatus and switchingover of the toll line are accomplished when the preferred subscriber ST lifts his receiver and momentarily-depresses the key AT athis station. When he lifts his receiver, relay A in the switch-over apparatus is energized over the subscribers loop by way of closed contacts 4: and 5.9 of the relay S. Relay A1 (bottom center of FigrZ) is operated by closure of contact 6a of relay A.

To indicate that the equipment is ready to: be seized for normal operation, the preferred subscriberreceives the dial tone WZ over the closed "contact 9a, repeater U1 and actuated contacts 13a, 14a.

Depression of key AT'operates the relay E over "the contact 15111 which has been actuated uponenergization ofrelay A1. Relay E closes its contact 19e-to establish a holding-circuit for itself. Contact Zlle disconnects the control conductor 1' comingfrorn the sound frequencyreceiver TE. Contact 21:: closes a circuit for 27t and 28L switch the toll line over tothecalling preferred subscriber. Contact 1011 connects the busy tone B2 to repeater U1 which in turn, transmits the busy tone over contacts 11t, 12t to'the cut-'ofi portionfof the'toll line, leading to the toll position; At the same time, the-busy lamp BLl associated with the toll line is'operated at the toll position by closureof contact 3111 in apparatus Um. This lamp indicates seizure of the toll line in gen- "eral. 'Seizure by the preferred subscriber in particular is indicated in addition by 'a busy lamp BL 2 in the service unit BS likewise located at tolljpositiom which lamp is operated by closure of contact 32L Relay B1, by actuating its. contacts 33221 and 34111,

itransrnits a sound frequency signal, indicating seizure of the switch-over apparatus, to the other end of the toll 'line.

This seizure signal is generated in the sound frequency generator TG; the length 'of the seizure pulse is 'determined by two condensers C1 and C2 co-operating "with a relay V. During idle periods, these condensers are charged over contact 37e and contacts 390, 40b respectively. Upon seizure, the condensers are connected in parallel over contacts 37e and 38:21. Upon operation ofrelay B,'the parallel condensers are discharged through the Winding of relay V so that the latter is maintained energized by the discharge current for a well-defined interval.

In the meantime, relay T1 has disconnected winding I of relay B at contact 35t1, but relay B remains energized by its winding II for a period of time governed by contact 36v of relay V. Relay B has opened the circuit for relay A1 at contact 7b, but relay Al is maintained operative for the time being over contact 73b1.

Upon release of relay V, relay B likewise deenergizes. The contact 4% of the'latter connects the condensers C1, C2 for recharging. As contact 23b opens, relay B1 is denergized, shifts its contacts 33b1, 34b1 and thus terminates the transmission of the seizure signal pulse.

In the switch-over apparatus at the other end of the line, the seizure signal pulse is transmitted through the preamplifier VV (Fig. 1) to the sound frequency receiver TE, and after rectification, the pulse is transmitted over contact 41i (Fig. 2) to the relay repeater unit 'Ue '(Fig. 1) of the switch-over apparatus Um. In the latter, the relay B (winding I) is energized, and after some delay, the relay D is operated. Contact 40b connects the charged condenser C2 to relay V, and when 'rel'ay D operates, its contact 45d also connects the charged condensers C3 and C4 to the relay V, the latter remaining in operation until the three condensers have 'been discharged. The energizing circuit for winding I of relay B has been opened at contact 42d but relay B is maintained operative by its winding II under the control of contact 36v.

Closure of contact 25d energizes relays T and T1 which, as already described, switch the toll line over to energized over its contact 50c. Relay C maintains relays T and T1 operated over its contact 260.

Upon operation'of relay C, relay R 1 is energized over contact'SZc; by its contact 3r1, relay R1 applies 2 cycle ringing current to the line of the called preferred subscriber. This ringing current may be transmitted con .tinuously or intermittently. At the same time, the idle signal F2 is connected over contact 53r1 to the repeater is still being held, relay C is now short-circuited over contacts 50c, 54b and 57x and releases. Relay C in turn contacts 44x and 21e.

4 U2 and is thence transmitted over the toll line to the calling preferred subscriber.

When the called preferred subscriber lifts his receiver, relay A is operated, either by the D. C. source of ringing current during ringing, or directly from a source or" D. C. during intervals between ringing signals. Contacts 13a and 14a complete the connection of the toll line to the called subscriber, and disconnect the idle signal FZ. Contact 6a operates relay A1 which disconnects the ringing relay Rlat contact 51:11. 7

When the called preferred subscriber replaces his receiver at the end of the conversation, the resultant interruption of the subscribers loop deenergizes relay A. Relay A1 remains operative over contacts 530 and 54a1. The switch-over apparatus remains seized and the toll line remains connected to the preferred subscribers.

Release of the switch-over apparatuses and switchingback of the toll line will not take place until the calling preferred subscriber 'replaces his receiver, thereby initiating the transmission of a release signal pulse. The relay A of the switch-over apparatus'on the calling side 'releases and interrupts, at contact 6a, the holding circuit for relay A1 so that the latter also releases. At contact 59a1 of the latter, the circuit for winding I of relay B is then closed, and this relay in turn operates relay Bl over contact 23b. As already described,

contact 40b causes relay V to be energized for the period during which condenser C2 is discharged. Relay B1 interrupts the circuit of winding I of relay B at contact 58b1, but relay B remains energized by its winding II turn releases relay B1 by opening contact 23b, whereby the transmission of the release pulse is terminated.

' 7 Relay E, which had been held operated over contact '16b after contact 15111 opened, is deenergized upon release of relay B and-releases with some delay. Relay X continues to be held after release of relay B1 until relay E also releases, the holding circuit for relay X including Opening of contact 22e deenergizes relays T and T1,

which release with some delay; this switches the toll line back to the toll position and disconnects the busy'tone BZ and the busy lamps BLl and BLZ. The switch-over 'apparatus is ready to be seized anew. a

In the switch-over apparatus on the called subscribers side, the sound frequency receiver TE applies ground potential to the control conductor i over contact 411' while V can be operated by the charged. condenser C3. Relay -X is operated over contact 55d and continues in operation by means of its holding contact 56x. Relay B, whose winding I was. disconnected at contact 42d upon operation of relay D, is maintained operative by its winding H until relay V releases. 7

Finally, relays V and B are released. Since relay X disconnects relay A1 at contact 53;. Relays T and T1 continue to be held operative after release of relay C, the holding contact being 25d. When relay D is restored 'at the end of the release pulse, the holding circuits for relays X, T and T1 are interrupted so that these relays are restored. Release of relays T and T1 switches the In the event of failure of the current source BBl or of a fuse, or upon breakdown of the 'pre arnplifier, the

sound frequency receiverfor the sound frequency gen erator, the normal operations thus far described'are no longer possible. The occurrence of'such trouble in the switch-over apparatus isautomatically indicated in the service unit BS at the mu position. The exchange operator thereupon actuates a key in the service unit and threby conditions-the apparatus for emergency operation. Battery BB2 constitutes the source of current supply for this emergency operation.

If the pro-amplifier, the sound frequency receiver or the sound frequencygenerator in the switch-over apparatus is the cause ofthe breakdown, it results in openingof contact or contacts we and thus opening of the holding circuitfor relay AL. ()pening of contact 2111 then opens alsothe holding circuit for relay S. Both relays are thusrestored.

If the trouble isin-batter y'BBl or in a fuse, relays AL and S are-likewise restored;

Afiashingcontact 60f1 (bottom'righ't' of Fig. 2) closes a flashing circuit for control lamp UL in the service unit (Fig. 3). The toll operator thereupon actuates the key TU, which energizes the relay U in-the switch-over apparatus Um of Fig. 2 in a. circuit from. ground, key contacts TAII and TUIT, conductor 5; relay'U to battery BB2. Contacts 2911,- 30a of this relay cause the extension of the tollline to-the preferredsuhscriber. At-the same time, busy lamp-BLI- at "the toll position is connected at contact 721:. Control lampUL is disconnected upon opening of contact 611:.

Before actuating the key TU, the toll operator notifies the exchange at the other end of the line that there is trouble in the switch-over apparatus, requiring the exten sion of the line to the preferred subscribers; the operator at the other end must likewise actuate the key TU and effect the switching-over already described. At the same time, the circuit for relay S is interrupted, and this relay deenergizes. However, since the switch-over apparatus at that end of the line is assumed to be in working order, its relay AL remains energized. In the associated service unit, the control lamp 'UL is maintained operated over contacts 62a1 and 63s. As this lamp is of no significance at that end of the line, it may be disconnected by actuation of a switch NG in the service unit.

When the preferred subscriber thereafter lifts his receiver, he actuates relay N over his loop circuit. Contact 66rd of the latter connects the busy lamp BL2 in the service unit. No dial tone or other audible signal is transmitted. If the subscriber, having lifted his receiver, then depresses key AT at his station, the closed contact 6721 in the switch-over apparatus energizes relay Q. This relay produces an outgoing ring, the length of which depends upon how long the key AT is being held depressed.

Depending upon whether the switch-over to emergency operation has or has not yet been efiected at the service unit, the ringing current emanating from the preferred subscribers station is transmitted either to the toll line or to the service unit at this subscribers own toll exchange. Ringing may be effected at will either as a cycle ring or as a D. C. ring, depending upon the circuits at the toll position. By way of illustration, there will be described hereinafter, first, a 25-cycle ring to the service unit, and second, a D. C. ring to the toll line.

If the switching-over to emergency operation because of a failure has not yet been carried out, a call by the preferred subscriber causes actuation of the call drop AK in the service unit. Ringing current is applied over contacts 68q, 69q in the switch-over apparatus. The actuated call drop in the service unit operate contact at: (Fig. 3) and ther by connects an audible signal Schn to alert the operator. This insures that the preferred subscribers call cannot be disregarded in cases of equipment failure. In this case, points 6 and 7 on the one hand, and points 8 and 9 on the other hand, are interconnected (see right-hand center portion of Fig. 2).

In the case of a D. C. ring to the toll line, or more specifically to the ring repeater inserted between the 6 switch-over apparatus and the toll line, negative battery is applied to the b conductor of the line duringringing. Negative battery is applied over contact 69q of link L3 and contact 3th: of link L2 to the b' conductor of link L1. In this case, points 9 and 10 are interconnected.

In the switch-over apparatus, assumed to be conditioned for emergency operation, at the' other: end of the toll line, only therelay U and under certain circumstances also the relay AL, are operated. The ZS-cycle ring is either transmitted direct to the switch-over apparatus, or if a ring-repeater is inserted, a D. C. ring is passedon to this apparatus. In either case, relay R in the apparatus is'energized.

If for any reasonthe apparatusshould not have been switched over for. emergency operation, the incoming call from the preferred subscriber arrives at the toll position like a normal toll call. At the toll position, the necessary steps are then taken to switch over 'to the calledpreferredlsubscriber. Thus, just as in-the case of outgoing calls, a preferred subscribers callcannot be lost inincomingtrafiic either. I

Relay R. remainslenergized for the duration of ringing and, during this period; connects relay R1 by means of contact 71:. Contacts 64x1 and 651' of relay R1 transrnit the ringing. current to the preferred subscriber. If the; called subscriber answers during an interval between rings; relay 'Niwill beenergize'd overhis loop as already described, and this relay, by opening its contact 7011, prevents any further calls from reaching this subscriber. Contact 66111 of the same relay operates busy lamp BL2 in the service unit.

At the end of the conversation, the receiver is replaced. Relay N is thereby restored and disconnects busy lamp BL2. The toll line remains connected for emergency operation until the toll operator switches back to normal operation by returning the key TU to its initial position.

When the trouble has been removed and the switchover apparatus is fully operative again, this is indicated at the exchange operators position. Relay AL is againoperated and, by its contact 62a1, connects control lamp UL in the service unit. The operator then returns the key TU to its normal position. Relay U in the switchover apparatus is released. This causes the toll line to be connected through to the operators position and disconnects the busy lamp BLl at contact 7211. Thereupon, the IN switch of the service unit is momentarily actuated to energize relay S of the switch-over apparatus; this relay then establishes its own holding circuit by closing its contact 1s, and effects the circuit connections described before.

As shown in Fig. 3, the auxiliary service unit (BS in Fig. l) is equipped with circuit means permitting the operator to converse with the preferred subscriber. This may be desirable, for example, for operational or other reasons, prior to switching-over to the emergency operation.

Actuation of the key TA interrupts the holding circuit for relay S in the switch-over apparatus. The preferred subscribers line link LT is then switched through to link L3, leading to the service unit, over contacts 4s and 5s. The operators hand set BA is connected to link L3 over contacts TAII and TAIII.

Calling of the preferred subscriber from the service unit is efi'ected by depression of ringing key RT; contacts RTI and RTII of this key apply ringing current to link L3. This current energizes relay R in the switch-over apparatus, and this relay in turn connects relay R1 at contact '71r. Contacts 64r1 and 65r1 insure transmission of the ringing current to the preferred subscriber.

This arrangement permitting conversation between the operator and the preferred subscriber may also be employed for the purpose of notifying the subscriber before the switch-over apparatus is switched back from emergency to normal operation.

As will be apparent from Fig. 2 (top right-hand co r-- 7 '7 ner), the preferred subscribers station is equipped with a visible signal S1 which is actuated over contact 63s in' the'sWitch-over apparatus and which indicates to the preferred subscriber the occurrence of a breakdown in the switch-over apparatus, or the switching-over of the circuits to emergency operation.

It will be clear from the foregoing explanations that the manner of using the apparatus by a preferred subscriber is the same for emergency as for normal operation. After lifting the receiver, the, subscriber in either case depresses a key which, in normal operation, causes seizure of the two switch-over apparatuses and automatic calling of the preferred subscriber at the other end of the toll line, while in emergency operation it causes this preferred subscriber to be called direct;

Changes may be made within the scope and spirit of the appended claims.

We claim: 7

1. In a telephone system having normal subscribers and preferred subscribers and having a trunk line for two-way trafiic terminating at the opposite ends in operators positions and having switch-over apparatus at each end thereof for extending such trunk line to a preferred subscriber, actuating means at each preferred subscriber for initiating the operative actuation of the associated switch-over apparatus to extend a call over said trunk line, signal means disposed at each operators position '8 for indicating to the corresponding operator failure of the respectively associated switch-over apparatus to extend said trunk line to the corresponding preferred subscriber responsive to the operation of said actuating means by such subscriber, means controlled by the operator for switching the corresponding trunk line to such preferred subscriber, control means for connecting a ringing current source to the corresponding preferred subscriber, and means operable responsive to the operation of said actuating means by said preferred subscriber for transmitting ringing current to the called subscriber or to said operator so' as to call said operator in the event of failure of said operator to extend said trunk line responsive to the, actuation of said signal means;

2. A system and co-operation of elements as set forth in claim 1, comprising means for connecting an emergency current source to supply current'to said preferred subscriber incident to connecting said ringing current source thereto.

References Cited in the file of this patent UNITED STATES PATENTS 2,332,290 Baumfalk Oct. 19, 1943 2,350,193 Rhoads May 30, 1944 2,350,873 Busch et a1. June 6, 1944 2,375,678 Newstedt May 8, 1945 

